I usually go to short stories, or old sword and sorcery novellas. For the former my go to stories are Lovecraft's Cthulhu Mythos, Robert E Howard's Conan, and Isaac Asimov's Robots. For the latter I prefer Michael Moorcock's Elric of Melniboné, Fritz Leiber's Fafhrd and the Gray Mouser, and Jack Vance's Dying Earth. If I'm feeling uninspired or experiencing a block, knocking out a few of these stories always sets me straight. They take next to no time to read and are great fun. I don't get tired of rereading them.